Wind tunnels are well known in the art. Wind tunnels are available in many types and styles depending upon the needs of the user. These include subsonic wind tunnels with and without return flow, transonic wind tunnels with and without return flow, vertical subsonic wind tunnels with and without return flow, supersonic and hypersonic wind tunnels with and without return flow, and compressible flow wind tunnels.
Vertical wind tunnels can be used for simulating skydiving and other human flight applications. For examples, see U.S. Pat. Nos. 5,655,909 and 6,083,110. Fliers in a vertical wind tunnel are free to move about inside flight chamber, it is therefore necessary to constrain their movement to appropriate parts of the system. While it is possible to put a safety net on either the upstream or downstream ends of the flight chamber, or both, using standard cables, these produce an enormous amount of drag which creates noise and increases the power required to attain any given speed. In fact, such a pair of nets can consume as much as 30% to 50% of the total power required to operate such a wind tunnel.
It is also helpful to have a woven grid of cables at the bottom or upstream end of the flight chamber for use as a standing platform when the occupants are not flying. This “cable floor” provides a convenient work platform for the safety officers or instructors in the flight chamber.
Therefore, for the above safety and usability reasons, it is desirable to have a cable floor/safety net made from cables with the lowest amount of aerodynamic drag possible for a given strength and diameter. In addition to wind tunnels, there are any number of applications employing cables moving through the air or air flowing over cables in which a simple and inexpensive reduced drag cable could provide substantial benefits.
Low drag cables with flat or airfoil shaped cross sections are know in the art and are used frequently in the aircraft industry. However, these are not useful in a woven cable floor for a vertical wind tunnel because it is difficult to keep such cables oriented properly in relation to the airflow. Furthermore, the downstream end of such a flat or airfoil type cable is pointed. Since it is the down stream end that a person falling onto the cable floor/safety net will land on, this type of cable is not safe for this type of application. The prior art airfoil type of cables cannot be used in some other types of applications where low drag cables would be desirable, for similar reasons of orientation, stability, cost or injury potential.
Vertical wind tunnels used for freefall simulation often have to operate in noise sensitive environments such as amusement parks and shopping malls. Horizontal testing tunnels can be located away from the crowds where they are free to make as much noise as is necessary. Therefore improvements that reduce the noise generated by the device are of a benefit. The cable floor/safety net is a significant contributor to the overall noise emitted from a vertical wind tunnel.
As amusement devices, freefall simulators must compete with other amusements on the basis of price and can often be operated on a near continual basis. These two factors make energy efficiency critical to successful commercial operation of a freefall simulator. Energy efficiency is much less important for horizontal testing tunnels in which one often takes hours or days to set up an experiment and then only runs the tunnel for a few minutes to collect the necessary data.
To make a commercially viable vertical wind tunnel for skydiving simulation, it is desirable to (1) move enough air and do so smoothly enough to adequately simulate freefall for one or more persons in the flight chamber; (2) with a device that is short enough and quiet enough to be located where large numbers of potential customers tend to be; and, (3) at power consumption levels low enough to make the price of the experience acceptable to the public. Similarly, constraining the occupants to the safe areas of the wind tunnel without increasing drag and power consumption is important.
The foregoing example of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.